Upper Serangoon Road Viaduct Owner/Client:   Land Transport Authority Main Contractor:   Wayss & Freytag-Econ-Chew Eu Hock J.V. Main Consultant:   Land Transport Authority Structural Consultant:   Engineering 2000 Scope of work by BBR:   Design and build of viaduct including pier, crosshead, diaphragm, superstructure & approach structure Bridge Data:   Length 1.5km, Width 12.4m, 4-lane carriageway Contract Sum:   $26.13 million Years of Execution:   1997 to 2001 Project Description: The viaduct is a 1.5km long dual 4-lane elevated carriageway running in parallel above the existing Upper Serangoon Road and crossing 2 major road junctions at Braddell Road/Bartley Road and Boundary Road/Upper Paya Lebar Road. The scope of works consist of design and construction of the viaduct beginning from Upper Aljunied Road and ending at Yio Chu Kang Road including piles, pile caps, piers, crossheads, box girders, abutments, retaining walls, approach structures and slabs, drainage system and temporary shoring and falsework. The design concept of the viaduct consists of post-tensioned, cast-insitu twin-cell box girders supported on a single central pier in the transverse direction. The viaduct comprises of 40 spans and is divided into 4 sections, with each section acting as a continuous frame structure over 8 or 12 spans. The length of one typical span is between 34.2m and 36.5m. The depth of the concrete box girder in a typical span is 2.2m. The spans at the 2 crossings, Braddell Rd/Bartley Rd and Boundary Rd/Upper Paya Lebar Rd, are 70m and 50m respectively where the maximum depth of the concrete box girders is 3.0m at the pier. The construction methods consisted of constructing the typical spans on an Advanced Launching Girder (ALG) with system formwork for span-by-span cast-insitu construction; and constructing the 2 crossings using the cast-insitu segmental Balanced Cantilever construction method. This is the first time ALG with system formwork is used in Singapore and it has demonstrated the effective use of this construction methodology in the viaduct construction to achieve quality finishes. The Advanced Launching Girder is a 850 ton steel structure specially designed and fabricated for the cast-insitu construction of 33 of the 39 spans of the viaduct. Firstly, the piers and the cross heads are constructed in advance of the ALG. For the construction of every span, 4 numbers of formwork units are adjusted, raised and suspended on the transverse trusses using Maccalloy bars (high tensile bars) in conjunction with the hollow ram jacks. After the formwork units are in placed, fixing of reinforcement, placing of ducts and concreting will follow. The concreting of the north-bound and south-bound viaducts have to be done simultaneously. When the structure achieves a concrete strength of 30MPa, the stressing of the tendons will begin. Upon complete transfer of load to the starting elements and piers, the formwork units will be dismantled and placed on the working platform. The entire ALG will then be jacked to the next span. This cycle is then repeated. The Segmental Balanced Cantilever Method is used to construct the spans over the Braddell Road/Bartley Road and Boundary Road/Upper Paya Lebar Road underpasses. The spans of the viaduct at these areas are 70m and 50m respectively. The method features segmental construction of 3.4m long segments. One segment to the left of the pier is first constructed and then stressed against the crosshead, followed by the corresponding unit on the right, which will also be stressed against the crosshead. The sequence is then repeated. Finally, there will be additional prestressing to provide continuity to the overall frame structure. Video animation of Advanced Launching Girder (14.7 MB) and Balanced Cantilever Method (8.2 MB)

Another Bridge Design and Construction Project by the BBR Group

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